In the manufacture of electrical coils, particularly large inductance coils or transformer windings involving relatively large gauge enamelled copper wire or rod, the coil is wound under tension on a winding arbor and the enamel insulation, being somewhat frangible, has a tendency to chip or crack on occasion as the relatively stiff copper wire is wound, thus forming shorted turns. In most cases, such shorts are not detectable by visual inspection, so that a short is not detected until after the coil has been fully wound, finished, and late subjected to an electrical acceptance test. In such cases, it is too late to repair the coil easily, as the short is then covered and difficult to locate.